the newer style adjustable reamers with multiple straight blades rung around a center post with a band on top and bottom holding the blades to the shank are garbage. i have some of the old adjustables though that work fairly well. they are spiral flutes, and the vales in the flutes are cut through to the cored center of the reamer. a set screw is on the end and you can squeeze the blades open in the center of the blades by tightening the set screw. they work well for certain jobs and hold fairly tight tollerances but the hole cannot be blind and the reamer can only expand past its nominal size something like .010 give or take. might be more i have just never done it on mine.